Currently, the main illumination instruments are still incandescent lamps (and also the energy saver fluorescent lamps) since most families, offices and public places still employ the base structure for the incandescent lamps, and also the newly developed LED illuminations are still not popular. A conventional lamp is illustrated in R.O.C. Patent No. M305303, entitled “Structure improvement of fluorescent bulb”, whose abstract disclosed that “The present application is related to an improved fluorescent bulb structure so as to provide a more practical efficacy, including two light permeable half plastic housings, a fluorescent tube, a positioning base, an auxiliary sleeve, a circuit board; and a conducting head, wherein the circuit board is fixedly mounted on the positioning base and the auxiliary sleeve in advance, and then assembled within the conducting head and the housings for reducing the total volume, and also, the plastic housings which are not easily broken can improve the usage safety.” The fluorescent bulb is composed of a lamp housing, a positioning base, a fluorescent tube, a conducting head, a circuit board, and electronic components connected to the circuit board, wherein the lamp housing is consisted of the two light permeable half plastic housings, and the two light permeable half housings have plural heat dissipating holes mounted thereon for providing heat dissipating function. However, since the fluorescent tube is encapsulated in the lamp housing and the positioning base does not additionally provide the heat dissipating function, the exhausting of the heat produced by the fluorescent tube through the heat dissipating holes has to be achieved by air convection. But, based on the physical principle that hot air rises up, it is obvious the heat dissipating holes which are located at the lower portion of the lamp housing can not efficiently exhaust the heat. Besides, the encapsulated structure also lowers down the heat dissipating efficiency. Therefore, this is still improvable. Another disclosure, R.O.C. Patent No. M265535, entitled “Bulb Type of Daylight Lamp Composite Structure”, has the abstract described that “The present application is related to the structure of a daylight fluorescent bulb which provides an easier and rapider assembling manner for the daylight fluorescent tube, the housing and the metal head, and also achieves the efficacies of firmness and durability, including an integrally formed assembling/fixing component having threads, a plate, engaging pieces, and engaging openings, wherein through the threads, the engaging pieces, and the engaging openings, the daylight fluorescent tube can be rapidly and securely assembled without adhesives, and through the threads and the plate, the housing and the metal head can be screwed and positioned rapidly and firmly, thereby improving the efficacy and providing a great practicability.” The bulb lamp includes a daylight fluorescent tube, a metal head, an outer shell, an assembling/fixing component, and a ballast and starter. In this disclosure, although the daylight fluorescent tube is not sealed for providing a better heat dissipating effect, the ballast and starter is accommodated in the assembling/fixing component, which only provides several let-in holes for passing through the air and providing slight heat dissipating effect. Thus, the daylight fluorescent tube still might become overheated. Consequently, although the above-described applications do achieve the main objects thereof, the heat dissipating efficiency is still improvable for preventing the overheated situation from reducing the life of the lamp.